Mugabe, main opposition Movement for Democratic Change leader Morgan Tsvangirai and Arthur Mutambara — who heads a breakaway MDC faction — signed the agreement at a hotel in the capital, Harare, after weeks of tense negotiations.
Mugabe and Tsvangirai last week agreed the deal to end a deep political crisis compounded by the veteran leader’s disputed and unopposed re-election in June.
The deal is expected to split control of the powerful security forces that have been key backers of Mugabe.
The president, a former guerrilla commander, is likely to retain command of Zimbabwe’s strong army, but the MDC wants to run the police force.
Zimbabweans hope the agreement will be a first step in helping to rescue the once prosperous nation from economic collapse. Inflation has rocketed to over 11 million percent and millions have fled to neighbouring southern African countries.
Under the deal Tsvangirai will become prime minister and chair a council of ministers supervising the cabinet.
Mugabe’s ZANU-PF will have 15 cabinet seats, Tsvangirai’s MDC 13 and a splinter MDC faction three seats.
Mugabe, 84, who has ruled Zimbabwe since independence from Britain in 1980 will remain president and head the cabinet.
Analysts say the power-sharing deal is shaky and will require former enemies to put aside their differences and work closely to overcome scepticism, especially from Western powers whose financial support will be vital for recovery.
The two political rivals met on Saturday and agreed to share out the cabinet posts. The powerful state security ministry was abolished while the justice portfolio was split into two and a new prisons department was created.
The MDC wants to take control of ministries of home affairs in charge of the police, local government to oversee councils, one of the justice ministries, information and the finance ministry — giving it responsibility for rescuing the shattered economy.
In return, the MDC is ready to leave Mugabe’s ruling ZANU-PF in charge of other key ministries, including defence.
ZANU-PF and MDC negotiators met early on Monday to allocate the 31 ministries. Names of the ministers are likely to be announced later in the week, a government official said.
There would also be a national security council, replacing a joint operations command of security service chiefs who the opposition say were instrumental in organising a violent campaign that intimidated the opposition into standing down for the second round presidential election, allowing Mugabe to return to power.